Most tests which purport to distinguish performance of schizophrenics from that of other patient groups contain large elements of motor behavior. This is particularly so in perceptual tests where motility is a highly significant source of variance. Simple tests of psychomotility are indeed highly sensitive to intra-organismic variations. These tests, such as reaction time, tapping speed and dexterity, are stable and reliable and seem to be relatively independent of intellectual level (above a certain minimum), socioeconomic status, and race. Their ease of administration, relative refractoriness to practice and to motivational variables recommend them for use in determining clinical status and especially for monitoring the effects of psychopharmaeologic agents. This paper discusses a rationale for the importance of using measures of motility in assessing schizophrenic and other psychopathology. The presumed importance of motility lies in its critical role in the organization and control of many psychological processes including perception. Its role in monitoring effective and adaptive response to stimulus inputs, to executive intentions, and its central importance in regulation through feedback are emphasized. The involvement of the musculature in schizophrenia is underscored with reference to some significant research findings.